Piezoelectric device



PIEZO-ELECTRIC DEVICE Filed July 21, 1942 2 Sheets-ShrewI l CELL ULosEZ9 /v/ TRHTE' @ci 92 1945 R. vv. neem-rs 293369279 I PIEZO-ELECTRICDEVICE Filed July 2l, 1942 2 Sheets-Sheet 2 Patented Oct. 9, 1945 UNITEDSTATES PATENT OFFICE PIEZGELECTRIC DEVICE Raymond W. Tibbetts, Camden,Maine Application July 21, 1942., Serial No. 451,690 18 claims. (c1.1v1- 327) This invention relates to piezo-electric devices forconverting electrical energy into mechanical vibrations or convertingmechanical energy into electrical impulses.

Objects oi the invention are to provide a piezo-electric device whichwill convert acoustical vibrations into electrical impulses withoutsubstantial distortion, which may have any desired electrical impedance,which may be readily cut-from homogenous crystalline material, which issubstantially unaffected in its operating characteristics by temperaturevariation, which magnines the piezo-electric effect, which has increasedsensitivity, which has a high order of natural frequency, which issubstantially free from extraneous noises and which is generallysuperior to piezo-electric devices of the prior art.

In one aspect the present invention involves the combination of apiezo-electric slab which expands in one direction and contracts inanother direction when subjected to electrostatic forces, together witha toggle extending in one of the aforesaid directions along one side ofthe slab, means connecting the ends of the toggle with the slab so thatIexpansion of the slab in the direction of the toggle tends to straightenthe toggle, and an actuator connected to the toggle intermediate itsends. While the perimeter of the slab may have any desired shape, it islpreferably square with its two diagonals extending in the aforesaiddirections respectively. The toggle may comprise an integral piece ofiexible material bowed from end to end or bent in the middle, or it maycomprise two relatively sti? members pivotally interconnected at themiddle of the toggle, The actuator may be connected to a Cutting orreproducing stylus or a sound pro ducer or other device, depending uponthe use, and in some cases the actuator may be connected merely to aninertia element.

In a more specic aspect of the invention a toggle is provided on eachside of the device, one toggle extending in one f the aforesaiddirections along one side of the slab and the other toggle extending inthe other of said directions along the opposite side of the slab. Thuswhen the slab expands-in one direction and contracts in the otherdirection, the middle of one toggle moves away from the slab and themiddle of the other toggle moves towards the slab. Thus' by connectingthe actuator to the middle of each slab, the two toggles work .togetherin moving the actuator back and forth. While the actuator mayinterconnect the two toggles around the edge of the device, itpreferably comprises a pin extending freely through an opening in thedevice.

lll

While the ends of the toggles may be cemented or otherwise secured tothe sides of the slab, the device preferably comprises means fast to theends of each toggle and bearing on opposite edges of the slab.Preferably the latter means comprises a frame extending around theperirm eter of the slab, the frame being flexible to accommodate thepiezo-electric distortion of the slab. The flexibility of the frame maybe secured either by forming the frame of liexible material or, in thecase of a square or other rectangular frame, by pivotallyinterconnecting the sides of the frame at the corners. When using aframe a plurality of rectangular piezo-electric slabs may be fitted intothe samelframe, either in superposed relationship or in the same planeor both. When a frame includes a plurality of slabs in the same plane,the slabs are preferably separated from each other by spacers.

For the purpose of illustration typical embodiments are shown intheaccompanying drawings, in which Fig. l is a perspective view of acrystal from which one or more piezo-electric slabs may be cut;

Fig. 2 is a perspective view of a slab cut from the crystal;

Fig. 3 is a similar view leads mounted on the slab;

Fig. 4 is a perspective view of a complete unit;

Fig. 5 is a diagonal section through a unit such as shown in Fig. 4,illustrating one way of mounting the unit;

y Fig. 6 is aperspective view like Fig. 4 except in that each electrodeis divided into two parts;

Fig. 7 isa diagonal section similar to Fig. 5 showing a modification;

Fig. 8 is a perspective view of a modied togele;

Fig. 9 is a section like Figs. 5 and 7 showing a modication;

Fig. 10 is a plan view oi a frame;

Fig. 11 is a plan' view of a unitl adapted to fit in the aforesaidframe;

Fig. 12 is an edge view of the unit;

Fig. 13 is an edge view of a unit comprising two piezo-electric slabs;

Fig. 14 is a plan view of a frame with four lpiezo-electric slabsmounted therein in the same plane;

Fig. 15 is a plan view of the separator shown in Fig. 14;

Fig. 16 is a plan view of the piezo-electric aswith electrodes andindicated in Fic. 3 has a 295i assenso sembly shown in Fig. i4, with theelectrodes mounted thereon;

Fig. 17 is an edge in Fis. 16;

Fig. lo is an edge view ci a comprising two layers or" slabs;

Fig. 19 is a diagonal section oi an assembly formed or the parts shownin Figs. 1Q, 1l. and

Fig. 2li is an elevation oi one of the piezoelectric `units mounted in adevice ior'cuttina a record ci' the lateral-movement type or ior reproducing such a record;

Fig. 2l is a similar view of a device for use with records ci theverticaimovement type.

Fig. 22 is a section showing protective coatings applied to acrystalline unit.

'While any piezo-electric material may be used in the present invention,Rochelle salt crystals are preferred, such a crystal being shown in Fig.i in which a-e is the electrical axis, b-b the transverse axis and c-cthe longitudinal asis. In cutting a square slab from such a crystal foruse according to the present invention, crystal is so out that thediagonal lines m-m and n n bisect the angles between the axes b-b andc--o Thus when the slab expands along the line :ca -m, it contractsalong the line isf-vi and vice versa.

The crystalline slab for my piezo-electric unit may be or any desiredshape. However l prefer a plate having substantially uniform majorclivlew oi the assembly shown similar assembly rnensions, that is asquare plate, vand having thickness suitable to meet the mechanical andelectrical speciiications lor which the unit is to be adapted. l have`found for one application of my invention theta crystalline slab havingmajor dimensions of 1'? millimeters by i7 nullimeters and having meetsboth the mechanical and electrical requirements. A slab hanne: thesespecifications is very suitable lor a microphone in association with asuitable diaphragm. or for an ear phone as the unit has a sufficientlylovv capacitive im pedance at low audio frequencies to faithiullyproduce or reproduce thorn.

The slab or plate oi Rochelle salt crystal as hole il cut or otherwiseproduced through the central portion made by the intersection oi thelines 'm--m and iz- 71.v

with the elec Theaxis of this hole is parallel trlcal axis of the plateand is oi sufficient dialneter` to allow a ree clearance for theconnecting pin t, as shown in Fia. 4. The electrodes il and il areattached to the maior surfaces oi the crystalline plate by any suitablemethod. However i prefer to apply gold leaf electrodes in the mannershown and described in my Patent No. 2.287.953. It is desirahle'but notnecessary to remove a portion o the electrode at opposite corners of thecrystal. as shown at e--e and -f, in order` that the cement substanceused to secure the bow members t and (Fiss. 4 and 5) may have a betteradhesion to the crystalline surface. Removal oi the electrode at theabove points will also prevent piezo-electric action oi the crystal atthese points. The lead extensions il] and iti (Fig. 3) may be oi anysuitable material and attached in any suitable manner. i prefer howeverto use a thin strip of pure silver foil or sheet and to secure the leadsin electrical contact with the electrodes i and E by laying the lead endon the electrode and applying a small piece of tin ioll or othermetallic ioii by a thickness of .Old inch,

. Fig. l.

Lib

' surface ci the crystal cutting a Eil the use ci an adhesive such asasphelturn or Duco cement.

in 1 show one ci my crystalline plates on which a multiplicity ofelectrodes are essern- 'bled In this specific case there are twoelectrodes on each maior surface ci the crystalline plate. a nay thatthe electromotive iorces are additive; thus, when used in conjunctionwith a device to convert mechanical motion or vibrations into felectrical energy, substantially twice the voltage output may beobtained with a given mechanical loro The bow elements are constructedand assembled in the manner as shown in Figs. nl and 5 or The bowelements may be made oi any suitable material of a somewhat exiblenature, such as Bakelite, metal or other material, or they may be madefrom a section of the same crystalline material as that of thecrystalline plate E prefer however using a rlat strip of Bakelite sincethis material can be readily fabricated and iornied and has a lowspecific gravity, thus elimina-'Ling as much as possible inertia effectsof the hows while vibrating in a plane parallel with the electrical axisoz" the crystalline plate 2. The degrees or arc oi the bows isdetermined by several factors-among which is the use to which thepieaouelectric unit is adapted. In practice l. ilnd, when the unit' isto be used to convert electrical impulses into mechanical motion orvibrations, about one millimeter clearance ci the highest point ci thearc of the bow, which is at its substantial central portion from thesuriace ci the crystalline plete is very satisfactory. When used as amicrophone unit and being driven by a, suitable diaphragm lor associatedwith a phonograph stylus the clearance between the bow at its highestpoint may be somewhat less than one millimeter.

The 'aow elements t and l are cemented by any suitable manner firmly tothe crystalline plate at the points e-e and f--f (Fig. 3) and as shownby the cemented portions i5 and it (Fla. 5). The bow members d and i arerlxed on opposite sides o? the crystalline portion il and are orientedat gli degrees to each other, with the chord with the are ci the bows.At the approximate center of each bow member a hole 2i is provided, thishole being lust large enough to accommodate the pin member?) of Pigs. dand 5. After the bow elements have been cemented in place, the pin d ispassed through the holes 2l oi the bow ele ments and is cemented by anysuitable cement, such as for example Duco cement, to the bow members ati3 and it oi Fig. 5. The hole il in the crystalline plate (Fig. 3)provides an ample clearance with the pin t (Fig. 5). The pin il may bemade of any suitable material having a lon' specific gravity. i nd harddrawn aluminum to be a suitable material for this purpose. Since the pinvlbrates or moves in a direction parallel to its long axis, connectionis made by the pin member to the acoustical diaphragm or other movingmember or member to be actuated.

'The supporting members t-lt-ii and i2 ci Fia. i may be made of anysuitable material havlng elastic properties, such as for example,rubber. viscose etc. These are cemented or otherwise secured to thesurface oi the crystalline portion at two opposite corners and to thesurface oi the two ends of the bow member l, as in Fig. Il. The bovfmembers may be made longer than the diagonal of the crystalline plate,thus causing an extension These electrodes are connected in such of thebow members beyond' the spices or the crystal portion. .In this case thesupporting sedare erly to the pin. The flexible supporting pads 38 and33, usually two in number, are disposed one near the end of the bow ortoggle member 38 and the other at a point about midway of the member.These pads are cemented to a suitable base 31. To the opposite end ofthe bow or toggle member 3G a pin or other suitable driving connection32 is attached. This in turn may be connected to an acoustical diaphragm3| or other device, to drive the piezo-electric unit or t be driven byit.

In Fig. 11 I show a plate of vpiezo-electric crystalline material 43such as Rochelle salt, together with its electrodes and leads 48 and 49and having a hole 44 pierced centrally with the plate through which aconnecting pin may pass freely. The frame shaped member 42 of Fig. 10may take the shape as shown having suitable slots at the apices. Thisframe member may be made of any suitable somewhat ilexible material suchas Bakelite which I have found to be satisfactory for the purpose. Theframe may have any suitable dimensions depending on the use to be madeof the assembled device. In general the frame is made the approximatethickness as that of the assembled crystal plate or plates and itsinternal dimensions may nt closely at all points of the crystal edgesand cemented thereto securely by any suitable cement such as Duco cementor the frame may have clearances at various points, only being securedby cement at suitable points along the crystal edges which in generalwill be near the apices of the crystal or crystals.

In Figs. 11 and 12 I show the crystalline element 43 assembled with itselectrodes 48 and 41 and their attached leads 48 and 49. This unit maybe made in the same manner as I have pre viously described or in anyother suitable manner.

In Fig. 13 I show a modification of my invention in which a plurality ofpiezo-electric plates and their electrodes may be placed in parallelposition; that is, the plates may be arranged with their adjacent majorsurfaces in contact and se curely cemented together as by Duco cement,or they may have separation between them, the electrodes being so poledthat the several piezo electric elements operate in like directionssimuln taneously or in any other suitable manner. This multiplecrystalline unit may be assembled in the trarne-like portion as shown inFig. 10 and Fig. 1 9 or it may have the bow or toggle elements attacheddirectly to the crystalline surfaces as previously shown and described.

A plan View oi' another modiflcation of my invention is shown in Fig.la. This arrangement of crystalline elements provides for a multiplicity0l.' elements arranged in a common plane and having a separator 58 ofsuitable material such as Bakelite. All of the crystalline elements areso poled that they act as one crystal or they may be connected in anysuitable manner. Each crystalline element is cemented in position in amanner analogous to that described in Fig. l0. The hole Il of the detailof the separator 58 as shown in electric Fig. .i6 is a plan view of themultiple crystalline element as shown assembled in Fig. 14 and Fig. 1'1Vis a cross section of the same. The crystalline elements fili, Gl, @Eand G3 are provided with electrodes and attached leads; however onelarge electrode may cover all of the crystalline elements on each sideof the assembly.

In Fig. 18 I show in elevation a modication of my invention in which aplurality of layers of crystalline elements G4 85-$6-61 are arranged,the top and other layers being arranged in a manner similar to thatshown in Fig. 16.

Fig. i9 is an arrangement of my invention in which I have shown asinglecrystalline element 43 assembled in a frame as in Fig. l0 and uponwhich bow or toggle elements 83-69 similar to the ones shown in Figs. 4and 8 are secured to the wings of the frame element 42 by cementing orother means. The pin 'i0 passes through the hole 44 and is secured tothe toggle elements at their central portions. The pin extensionprovides for attachmentl to any suitable device to be actuated or toactuate the piezo-electric device. The flexible pads 1| are secured tothe wings of the frame member near their extremities to provide supportto the assembled unit and to act as dampers of vibrations of the device.

In Fig. 20 I show my piezo-electric unit 18 in conjunction with alateral cut phonograph record mounted on a suitable base support 11. Thelever arm 18 is securely attached to the drive pin at 19 and the leverarm causes the stylus 80 to move when the unit and assembly is used as acutting or recording mechanism, and to be moved when the unit is used asal phonograph pick-up.

Fig. 21 shows my invention when used in conjunction with the hill anddale type of phonograph record. In this arrangement the stylus isdirected parallel with the driving pin of the piezoelectric unit thusresponding to the hill and dale impressions of the record groove whenused as a pick-up and causing hill and dale impressions on the recordwhen the unit is used as a recorder or cutting device.

Other uses `for my invention and its modiiications may be readilyappreciated by those versed in the art, as for example in associationwith an oscillograph device either ink or trace recording or by anoscillating mirror.

In those 'modifications involving a plurality of pairs 0i electrodes,either with a single piezoelement as in Fig. 6 or with a plurality ofelements as in Figs. 13, 14, 16, 17 and 18, the device may be used toset up electrical pulsations in one circuit in response to pulsations inanother circuit merely by connecting one circuit t-o one set of opposedelectrodes and the other circuit to another set of opposed electrodes.Thus in Fig. 6 lead 28 would be cut with one end connected in a circuitcomprising lead 29 and the other end connected to another circuitcomprising lead 3B.

When used in conjunction with an acoustical diaphragm for example, thepin of Fig. 5 is caused to move and vibrate, which in turn causes thebow members 6 and l to vibrate in a direction parallel to the electricalaxis and perpendicular to the major surfaces of the crystalline portion2. Since the resultant force of the up and down motion of the bows isperpendicular to the major surfaces of the bows and parallel :to theplane of the crystalline plate and the ends of the bows are securelyattached to the apices of the crystallme plate, the lengthening andshortening action or the bow members is trans= ferred to the crystallineplate in the directions of the long axis o the bow members and from apexto apex o the crystalline-portion, this being the mechanical axis of thecrystal. The change of length of the chord of the bows is much less thanthe amplitude of vibration oi the bows at the points where the pin Vtlis attached and thus a great multiplication of force is obtained, andwith a corresponding reduction of amplitude of extension andsimultaneous compression of the crystalline portion along the lines m-mand n-n. Since the bows are in opposition on either side of the crystalplate and at right angles to each other, whenv the upper bow lill isdepressed with aresultant lengthening of the of the bow and extension ofits attached the lower bow l is chord crystal, along the line mf-m,

caused to assume a greater arc with a conse quent shortening of itschord and compression of the attached crystal plate along the linerif-n. As the lines m-m and rif-n represent the active mechanicalaspects of the piezo-electric crystalline plate, a maximum ofelectrostatic force is produced between the electrodes attached to themajor surfaces of the crystalline. plate. Inas-v much as the bows aresecurely cemented to each. apex of the crystalline plate, any bowingaction of the bow elements must cause a'nding of the corners of lthecrystalline'plate, producing a most cup and crown action to the centralportion oi the crystalline plate. This convex-concave amplitude ishowever less 'than that ol the Ybows since the ends ci the crystal bendmuch easier than does the central portion of the crystal; therefore itis usually necessary to providethe clearance hole il o Fig.'3 to permitfree motion of the pin e o Fig, li. However insome applications it maybe desirable to fix the central portion of the crystal tothe pinat theirjuncture to give an increased siiness to the assembly.

As well as a waterproof coating of lacquer or other material on theassembly as shown in Fig. 3, it may be desirable to place the wholeassembly within a jacket or iiexible casing, such as for example arubber jacket produced by spraying Vultex (a colloidal vulcanized rubberproduct) over the whole unit assembly, allowing the pin' Y d to extendthrough the flexible casing.

The, iiexible supporting pads serve to anchor the unit to a suitable'supporting member or case.

These pads also serve to allow the slight exion' trode attached to eachmajor surface. With this l aseaave chanical force, that is, apiezo-electric unit having a higher order of sensitivity, thearrangement as shown in Fig. 6 may be preferable.

ln this amusement the electrodes til, 25, '2s and 2l constitute twoseparate elements applied to each ofthe major surfaces of thecrystalline plate. Ilhese electrodes are connected in series by the leadextensions 28, 2S, 3u. This arrangement operates very satisfactorily inconjunction with an acoustical diaphragm as a microphone for hearingaids and other devices requiring 'a high order of sensitivity but notrequiring a, low impedance source oras faithful reproduction oi the lowaudio frequencies. The electrode arrangements may be further divided, asfor example four separate electrodes may be applied to the fourquadrants of each major surface of the crystal and connected by suitablelead extensions in series, thus further increasing the electricalpotential at the nal leadterminals. It is also obvious to those familiarwith the art that pick-up stylus, phonograph recording stylus, or

any mechanical device such as for example an acoustical switch, to beoperated in conjunction with the piezo-electricdevice as hereindescribed and shown.

lviy piezo-electric device can also be mounted on a suitable base and ine. suitable case and without mechanical connection to the driving pin dof Fig. 4 or the driving pin 32 of'Fig. the case and base assemblyitself `being caused to vibrate, as for example, a vibration pick-updevice. In this arrangement a suitable weight may be attached to thedriving pin il or ,32, whereby the mechanical movements of the case and'base assembly causel the bow or toggle members to vibrate by virtue ofthe inertia effect of the small weight andthe inertia of the bow ortoggle members themselves. Thus in Fig. 'Z a weight W is attached to theupper end of the pin 3d and the unit is mounted in a casing 32' of thinBakelite or the like, the rubber pads corresponding to those of Figs, eand 5 being cemented to the casing as well as the unit. Such a device isparticularly useful in converting the vibrations of a body intoelectrical impulses because in use it need only be set on the body, thecasing vibrating with the body andthe weight W restraining vibration ofthe bows.

The detail shown in Fig. 8 represents a modification of the bow ortogglemembers. 'ln this type the flat,d slightly flexible material isbent at its center to form a wide obtuse angle, and on its major surfaceaspect it may be somewhat narrowed at its central portion to permit ofeasy flexion. Thus in action in association with the crystalline plate,the members assume a toggle arrangement the electrical potentialproduced by virtue of the piezo-electric action of the crystallinematerial 2 is relatively low under a. given condition of mechanicalstress; the capacitive impedance of the arrangement is howeverrelatively low due to the inherent properties of the Rochelle saltcrystalline plate and the relatively large electrodes l and E. Howeverwhen a larger electrical potential is desired from a given nieactionwith a consequent augmentation of the forces applied to the toggle-likemember in the direction perpendicular to its maior surface and in. adirection parallel to the long axis oi the member and applied to thecrystalline plate by virtue of its xation to the toggle members in themanner above described for the fixation of the other type member.

The mounting arrangement or" Fig. 9 provides for an increase in leveragedue to the arrangement and location of the supporting pads 38 and 39because had 38 acts as a fulcrum and Dad 39y acts as a fixed point. Whenthe connecting pin or member 32 is xed at the opposite end from thesupporting pad 39, a larger amplitude of the connecting pin and itsassociated acoustical diaphragm 3l, or other device to be actuated, isobtained. When the pin 32 is vibrated or moved through a certainamplitude, as for example by an acoustical diaphragm or phonographstylus, the resultant motion of the bows or toggles is reduced, with aproportional increase of force applied to the crystalline plate by thelateral elongation and shortenlng of the bow or toggle members.

Referring to Figs. l0, l1, 12 and 19, the operation of this modifiedform of my invention isas follows: The crystalline element #3 and itsassociated electrodes and leads 48 and 43 is mounted and securelycemented within the space provided by the frame member 42. The slots 42ain the wing portion of the frame member provide for flexibility of theframe memberA when it is dist/.irted by the action of the crystallineplate A3. Since any lessenlng of the dimension through m-m will causethe frame to lengthen through the direction n--n, I have provided anideal supporting member for the piezo-electric plate 43, the platemanifesting substantially the same clistortion properties whenfunctioning piezo-electrically as has previously been described. 'I'hebow or toggle members 68-59 are secured firmly to the portion of thewing members of the frame 42, external to the slotted portion andoriented in a manner similar to that shown in my unit of Flg.'4. The pin10 passing through the clearance hole M is ilxed securely to the centralportion of the bow or toggle members 68-69, thereby transmittingmechanical impulses to or from the bow members and in turn to or fromthe wing members of the frame portion, thus actuating the crystalportion within the frame or being actua'ted by it. 'I'he pads 1I provideas previously described and shown in Fig. for a flexible and dampingsupport for the assembly and the pad 15 reacts to dampen vibrations whenthis element is needed in certain applications, such as for example inassociation with an acoustical diaphragm when used as a microphone.

I have found that it is desirable to protect the crystalline portion or"my unit and its modifications from moisture since the piezo-electriccrystalline plate or plates are water soluble and moisture alters theproperties. I therefore coat the exposed surfaces of the crystal plateor plates and the electroded lportions iirst with a suitable liquidplastic such as for example cellulose nitrate in a suitable solvent.Then after cementing the various elements such as the bow or togglemembers or the crystal portion and its electrodes and leads within theframe member in the modiiled form oi my invention; I apply a final coatof' a solution of polystyrene in a suitable solvent. In Fig. 22 suchcoatings are shown as applied to the plate 2 of Fig. 2. Polystyrene hasvery low water absorbing properties and a very thin coat providesexceptional moisture-mooring for a device of this type. It is howeververy dilcult to irmly cement to surfaces coated with polystyrene. Itherefore apply the cellulose nitrate or similar material to the crystalportion first, cement to this coated surface and then apfirst to use itfor moisture-proofing soluble piezoelectricfcrystalline elements.

' I have also found vinylidene chloride to be a suitable substitute forpolystyrene in my process.

The crystalline portion shown in side view in Fig. 13, comprises two ormore piezo-electric crystalline plates arranged with surfaces adjacent.This arrangement provides for a greater applied force and by virtue ofthe greater capacity of a plurality oi single elements a lowerelectrical impedance may be obtained or the crystalline portions mayhave a greater relative thickness and thus maintain a given impedanceand gain a greater volume of piezo-electric material and consequentgreater applied force and dielectric strength. .All crystalline elementsmay be so poled that the mechanical forces are applied in the samedirections simultaneously.

The modification shown ln Fig. 14 provides for a plurality ofcrystalline portions all on the same plane and having a cross-shapedseparating member 58 al1 mounted Within the frame-like member 42. Thecrystal portions may be poled so that all crystals act or react in thesame directions as would one large crystal, thus the unit may beassembled with bow or toggle members or by any other means to secure anydesirable mechanical movement.

The modification shown in Fig. 18 is like the arrangement shown anddescribed in Figs. 14, 15, 16 and 17 except that this arrangementprovides a plurality of layers of crystal elements and demonstrates thesame electrical properties as the arrangement shown and described inFig. 13.

I have found my framed type of element assembly is well suited to theproduction of a phonograph recorder or pick-up by associating the de--vice with suitable connecting mechanism with a stylus. This is vequallytrue whether the pick-up or recorder is of the lateral-cut type or thesocalled hill and dale type. My piezo-electric device and itsmodications may be associated equally well with a mirror oscilloscope ora direct recording oscillograph and also equally well with an acousticalswitch, and it may be associated with an inertia weight fixed to thedevice pin or bow or toggle members and thus by vibrating the wholeassembly become a vibration pick-up, and many otherl devices requiring apiezo-electric element in its association.

From the foregoing it will be evident that my invention is to be calledbimorph device ol the prior art in which the stratum on one sidecontracts in one direction at the same time the stratum on the otherside expands in that direction, thereby causing the slab to warp.According to the present invention each stratum expands in the samedirection at the same time. Thus when the device comprises superposedlayers the corresponding diagonals of the respective layers extend inthe same direction so that the expansion at any instant is in the samedirection in each layer.

It is to be understood that the particular forms of apparatus shown anddescribed and the particular procedure set forth are presented forpurposes of illustration and explanation, and that various modificationsof said apparatusand procedure can be made without departing from myinvention as defined in the appended claims.

I claim:

1. In a device of the character described the combination of apiezo-electric slab which expands in one direction and contracts inanother distinguished from the sodirection when subjected toelectrostatic forces, a toggle extending in one of said directions aloneone side of the slab, means connecting the ends of the toggle with theslab so that expansion oi the slab in the direction of the toggle tendssubstantially and effectively to straighten the togglo, and an actuatorconnected to said toggle intermediate its ends.

2. in a device of the character described the combination of apiezo-electric slab which expands in one direction andcontracts inanother direction when subjected to electrostatic forces, a tosgleextending in one of said directions along one side of the slab, meansconnecting the ends oi the toggle with the slab so that expansion of theslab in the direction of the toggle tends substantially and edectivelyto straighten the toggle, and an actuator connected to said toggleintermediate its ends, said toggle comprising a lerible member whicharches away from the slab intermediate its ends.

3. In a device oi the character described the combination of apiezo-electric slab which exponds in one directionand contracts inanother direction when subjected to electrostatic forces, a toggleextending in one of said directions alone one side of the slab, lanothertoggle extending in the other of said directions along the opposite sideof the slab, means connecting the ends of the toegles with the slab sothat expansion of the slab in either of said directions tends tostraighten the corresponding toggle, and an actuator interconnectingsaid toggles intermediate their ends.

e. in a device of the character' described the combination of apiezo-electric slab which expands in one direction and contracts inanother "direction when subjected to electrostatic forces,

a toggle extending in one of said directions alone one side o the slab,another toggle extending in the other of said directions along theopposite side of the slab, means connecting the ends of the toggles withthe slab so that expansion of the slab in either of said directionstends to straighten the corresponding toggle, and an actuatorinterconnecting said toggles intermediate their ends, each of saidtoggles comprising a iiexible member which arches away from the slabintermediate its ends.

5. En a device of the character described the combination of apiezo-electric slab which expands in one direction and contracts inanother direction when subjected to electrostatic forces, a toggleextending in one of said directions alonel one side of the slab, anothertoggle extending in the other of said directions along the opposite sideof the slab, means` tast to the ends of the toggles and bearing onopposite edges of the slab so `that' expansion of the slab iny either ofsaid directions tends to straighten the corresponding toggle, and anactuator interconnecting said tos'- gles intermediate their ends.

` d. In a device of the character described the combination of arectangular piezo-electric slab which expands diagonally when subjectedto elect trostatic forces, a frame abutting the edge of the slab at eachcorner, the frame being gexible to accommodate the piezo-electricdistortion oi the slab, a toggle extending along e, diagonal of the slabon one side thereof, the ends of the toggle beine' connected to saidframe, and an actuator connected to the toggle intermediate its ends.

7. In a device of the character described the combination of arectangular piezo-electric slab which expands diagonally when subjectedto electrostatic forces, a frame abutting the edgeof the .nascere slabat each corner,the frame being einble to accommodate the piezo-electricdistortion of the slab, toggles respectively extending along the twodiagonals of the slab an opposite sides thereof, the ends ofthe togglesbeing connected to said frame, and an actuator interconnecting thetogeles intermediate their ends;

8. In a device of the character described the combination'of arectangular piezo-electric slab which expands diagonally when subjectedto electrostatic forces, an integral frame abutting the edge of the slabat each corner, the frame being made of exible material to accommodatethe piezo-electric distortion of the slab, a toggle extending along adiagonal of the slab on one side thereof, the ends of the toggle beingconnected to said frame, and an actuator connected to the toggleintermediate its ends.

9. in a device of the character described the combination of a exiblerectangular frame, a plurality of rectangular slabs tted into the framewith their corresponding axes extending approximately parallel to thetwo diagonale of the frame dii respectively so that the frame is exed bythe slabs conjointly when the slabs are subjected to piezo-electricdistortions, a toggle extending along a diagonal of the slab on one sidethereof, the ends of the toggle being connected to the corners oftheframe, and an actuator connected to the toggle intermediate its ends.

l0. In a device of the character described the combination of a flexiblerectangular` frame, a plurality of rectangular slabs iitted into theframe with their corresponding axes extending approximately parallel tothe two diagonals of the frame respectively' so that the frame is flexedby the slabs conjointly when the slabs are subjected to piezo-electricdistortionslsaid slabs lying in the same plane, spacers between theopposing edges of the slabs, a toggle extending along a diagonal of theslab on one side thereof, the ends `of the toggle being connected to thecorners of the frame, and an actuator connected to the toggleintermediate its ends.

l1. A piezo-electric device according to claim l further characterizedby elastic base members for supporting the device at its four corners.A

l2. A piezo-electric device according to claim l further characterizedby elastic base members for supporting the device, one at the extremityof said toggle and another intermediate the ends of the toggle, theaforesaid actuator being xed to the device near the other end of saidtoggle.

13. A piezo=electric device according to claim l further characterizedby an inertia weight xed to the actuator to cause the device to vibratebodily.

lo. In a device of the character described the combination of apiezo-electric slab which exbands in one direction and contracts inanother direction when subjected to electrostatic forces, the expansionat any instant being in the same direction in each stratum throughoutthe thicknesses oi the slab, a toggle extending in one of saiddirections along one side of the slab, means connecting the vends ofthetoggle with the slab so that expansion of the slab in the directionof the toggle tends to straighten the toggle, and an actuator connectedto said toggle intermediate its ends.

l5. A piezo-electric device comprising a slabA which expands in oneflatwise direction when subjected to electrostatic forces, a flexiblemember extending along one side of the device, and means interconnectingthe slab and member at the periphery of the slab, the member beingarched in sesame 7 said direction sc that it tends to straighten when -1arched in one oi said directions sc that it tends to the slab expandsasaioresaid. straighten when the slab expands in that direc- 16. Apiezo-electric device comprising a slab tion. I which expands in oneiiatwise direction when 18. A piezo-electric device comprising a slabsubjected to electrostatic forces and a flexible 5 which expands in oneatwise direction and conl l member extending along one sideoi' thedevice, tracw in another edgewise direction when subthe member beingcemented to the slab at the jected to electrostatic forces, a iiexiblemember periphery of the slab and being arched in said extending alongone side of the device, a flexible direction so that it tends tostraighten when the member extending along the other side of the desla-bexpandsasaforesaid. 10 vice, and means interconnecting the 4slab and 17.A piezo-electric device comprising a slab members at the periphery ofthe slab, the memwhich expands in one atwise direction and conbers beingarched in said directions respectively tracts in another edgewisedirection when subso that each member tends to straighten when thejected to electrostatic forces, a ilexibie member slab expands in thedirection in which it is e means interconnecting the sieb and members etRAYMOND W. means.

